i understand that there are potential environmental concerns, but haven't we been affecting the natural balance for millennia with the selective breeding of livestock and crops? you have to consider that there are also potential environmental gains. i'll give an example - you have a field of crops that is doused in pesticides, which not only effects the crop you are trying to produce, but all the surrounding vegetation and wildlife. in a field of crops that doesn't require pesticide, the surrounding wildlife is unaffected. the crop would not be a viable source of food for it's natural pests, but wouldn't that be the case with pesticides anyway? at least this way other food sources for the natural wildlife would remain. this is a very slanted example, but i just wanted to show that it can go both ways - gm does not mean that it has to have a negative impact on ecosystems, and could actually be engineered for environmental benefit.
as for health issues, i don't buy that at all. i have yet to see anything based on fact that suggests that gm crops are any more harmful to us than non-gm crops. i understand the science behind why it *could* happen, but i have yet to see any evidence that proves, or even suggests why this would really be the case. as i stated above, we've been selectively breeding for centuries and there are exactly the same set of pitfalls with this. you breed the two most pest resistant crops together over generations and you may see an increase of naturally occurring chemicals that are harmful to both insects and humans. we've been doing this for millennia and we're still here, so i don't see the problem.
i find it far more likely that health benefits such as increased levels of vitamins will make their way into genetically modified foods. the long term potential for what could be done with GM foods is pretty amazing, i'm not saying there won't be the occasional hiccup, but i genuinely don't believe there will be anything that we can't deal with, or anything that is widely above what we've seen with selective breeding. it's my personal opinion that it is little more than short sightedness that fuels this disdain for gm foods.